Variable displacement swash plate type compressor

ABSTRACT

A variable displacement swash plate type compressor includes a bearing, a thrust bearing, a lug plate and urging means. The urging means is placed between the bearing and the lug plate and has urging force for reducing thrust force applied to the thrust bearing. The bearing receives radial force and thrust force.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a variable displacement swashplate type compressor that is applied to a vehicle air conditioningsystem.

[0002] A compressor is installed in a refrigerant circuit for use in avehicle air conditioning system. The compressor compresses refrigerantgas therein. In a prior art of Japanese Unexamined Patent PublicationNo. 2002-13474, more specifically in FIG. 8 thereof, a typical variabledisplacement swash plate type compressor is disclosed for use in avehicle air conditioning system. A housing of the compressor includes afront housing, a cylinder block and a rear housing. The rear end of thefront housing is joined to the front end of the cylinder block. The rearend of the cylinder block is joined to front end of the rear housingthrough a valve mechanism that includes a suction valve plate, a valvehole plate, a discharge valve plate and a retainer plate. A plurality ofcylinder bores extends through the cylinder block so as to be parallelwith each other. The front housing and the cylinder block define a crankchamber therebetween. A suction chamber and a discharge chamber aredefined in the rear housing.

[0003] A single-head piton is accommodated in each cylinder bore forreciprocation. A compression chamber is defined in the correspondingcylinder bore between the corresponding piston and the valve mechanism.A first shaft hole extends through the front housing. A first bearing isinstalled in the first shaft hole. A second shaft hole extends throughthe cylinder block. A second bearing is installed in the second shafthole. That is, the first bearing is located frontward than the secondbearing. A drive shaft is supported by the first and second bearings forrotation. The front end of the drive shaft protrudes from the fronthousing and is connected to an external drive source such as a vehicleengine so as to be driven. A support spring is interposed between therear end of the drive shaft and the valve mechanism through a thirdbearing in the second shaft hole. The rear end of the drive shaft is incontact with the front end of the third bearing. The rear end of thethird bearing is in contact with the front end of the support spring.The rear end of the support spring is in contact with the front end ofthe valve mechanism. The support spring urges the drive shaft frontward.

[0004] A lug plate is fixed to the drive shaft in the crank chamber soas to integrally rotate with the drive shaft. A thrust bearing isinterposed between a front wall of the front housing and the lug platedin the crank chamber. A swash plate is supported by the drive shaft inthe crank chamber for rotation. A hinge mechanism is interposed betweenthe lug plate and the swash plate. Thereby, the swash plate issynchronously rotated with the drive shaft and is inclinable withrespect to a rotary axis of the drive shaft. Also, the pistons engagewith the periphery of the swash plate. Thus, the piston is reciprocatedin the corresponding cylinder bore in accordance with the rotation ofthe swash plate. A control mechanism is installed in the rear housingand communicates with the crank chamber, the suction chamber and thedischarge chamber. The control mechanism controls the pressure in thecrank chamber.

[0005] In the compressor, while the drive shaft is driven, the swashplate oscillates in accordance with the inclination angle of the swashplate and thus the piston is reciprocated in the corresponding cylinderbore. Therefore, refrigerant gas in the suction chamber is drawn intothe compression chamber, and the refrigerant gas is compressed therein,and then the compressed refrigerant gas in the compression chamber isdischarged into the discharge chamber. During the above process of thecompressor, if the control mechanism controls the pressure in the crankchamber, since the inclination angle of the swash plate is varied, anamount of the refrigerant gas discharged from the compression chamber tothe discharge chamber is also varied. That is, as the pressure in thecrank chamber is raised, the inclination angle of the swash platebecomes small and the discharge amount of the refrigerant gas isreduced. In contrast, as the pressure in the crank chamber is lowered,the inclination angle of the swash plate becomes large and the dischargeamount of the refrigerant gas is increased.

[0006] On the other hand, during the above process of the compressor,the first bearing and the second bearing receive radial force that isapplied to the drive shaft respectively in the front housing and thecylinder block. The thrust bearing receives compressive reaction forceof the refrigerant gas through the piston, the shoes, the swash plateand the lug plate in the front housing. In addition, in the compressor,the crank chamber and the second shaft hole are communicated via thesecond bearing, and the support spring is interposed between the rearend of the drive shaft and the valve mechanism. Therefore, the thrustbearing receives the pressure in the crank chamber and urging force ofthe support spring, which are applied to the drive shaft and the lugplate.

[0007] In the above prior art, however, since only the thrust bearingthat is placed between the front housing and the lug plate in the crankchamber receives all of the compressive reaction force, the pressure inthe crank chamber and the urging force of the support spring and rollingdiameter of the thrust bearing is larger than that of the first bearingand the second bearing, power loss of the thrust bearing is relativelylarge.

[0008] Meanwhile, in a compressor that is disclosed in the abovepublication, a cylindrical regulating member is fitted around a rear endof a drive shaft so as to have a slight clearance between thecylindrical regulating member and a valve mechanism without the supportspring in the shaft hole of the cylinder block between the rear end ofthe drive shaft and the valve mechanism. In the disclosed compressor, athrust bearing does not require receiving the urging force of thesupport spring. Therefore, power loss is reduced.

[0009] Even in the compressor, however, the thrust bearing stillreceives both of the compressive reaction force and the pressure in thecrank chamber. Therefore, the power loss is not sufficiently reduced. Inparticular, in a state that the pressure in the crank chamber isrelatively high and displacement of the compressor is relatively small,although the compressive reaction force is not so large, since the driveshaft is urged frontward by force caused due to the high pressure in thecrank chamber, the power loss in the state is not ignored.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a variable displacementswash plate type compressor whose power loss is reduced.

[0011] The present invention has the following features. A variabledisplacement swash plate type compressor is used in connection with anexternal drive source. The compressor includes a housing, a firstbearing, a drive shaft, a lug plate, a swash plate, a single-headpiston, a control mechanism and urging means. In the housing, a cylinderbore, a crank chamber, a suction chamber and a discharge chamber aredefined. The first bearing is accommodated on a front side of thehousing. The first bearing receives radial force and thrust force. Thedrive shaft is supported by the first bearing in the housing rotatably.The lug plate is fixed to the drive shaft in the crank chamber. Theswash plate is supported by the drive shaft in the crank chamberrotatably. The single-head piston is accommodated in the cylinder borereciprocably and is connected to the swash plate so as to reciprocate inaccordance with the rotation of the swash plate. The control mechanismcommunicates with the crank chamber, the suction chamber and thedischarge chamber for controlling pressure in the crank chamber. Theurging means is placed between the first bearing and the lug plate andhas urging force for reducing thrust force applied to the first thrustbearing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The features of the present invention that are believed to benovel are set forth with particularity in the appended claims. Theinvention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

[0013]FIG. 1 is a cross sectional view illustrating a variabledisplacement swash plate type compressor according to a first preferredembodiment of the present invention;

[0014]FIG. 2 is a partially enlarged view of FIG. 1;

[0015]FIG. 3 is a partially enlarged view of FIG. 1; and

[0016]FIG. 4 is a partial cross sectional view illustrating a variabledisplacement swash plate type compressor according to a second preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A variable displacement swash plate type compressor according toa first preferred embodiment of the present invention is applied to avehicle air conditioning system. The compressor will now be describedwith reference to FIGS. 1 through 3. In FIG. 1, a left side of thedrawing is a front side and a right side thereof is a rear side.

[0018] Referring to FIG. 1, the rear end of a cup-shaped front housing 2is joined to the front end of a cylinder block 1. The rear end of thecylinder block 1 is joined to the front end of a rear housing 7 througha valve mechanism that includes a suction valve plate 3, a valve holeplate 4, a discharge valve plate 5 and a retainer plate 6. The cylinderblock 1, the front housing 2 and the rear housing 7 form a compressorhousing. In the cylinder block 1, a plurality of cylinder bores 1 a, ashaft hole 1 b, a muffler chamber 1 c and an inlet 1 d are defined. Inthe front housing 2, a shaft hole 2 a is formed. The cylinder block 1and the front housing 2 define a crank chamber 8 therein.

[0019] Still referring to FIG. 1, a drive shaft 12 extends through thecrank chamber 8 and is supported by a first bearing 10 at the shaft hole2 a and by a second bearing 11 at the shaft hole 1 b rotatably. A shaftseal device 9 seals a clearance between the drive shaft 12 and the fronthousing 2. In the first embodiment, a tapered roller bearing is adoptedas the first bearing 10. Also, a radial bearing is adopted as the secondbearing 11.

[0020] As shown in FIGS. 2 and 3, the first bearing 10 includes an innerrace 10 a, an outer race 10 b, a plurality of rollers 10 c and a cage,which is not shown in the drawings. The drive shaft 12 is press-fittedinside the inner race 10 a so as to integrally rotate with the innerrace 10 a. The outer race 10 b is press-fitted into the front housing 2.The plurality of rollers 10 c is interposed between the inner race 10 aand the outer race 10 b. A rolling contact surface of the inner race 10a is formed on a cylindrical surface whose central axis is the same as arotary axis of the drive shaft 12. A rolling contact surface of theouter race 10 b is formed on a tapered surface whose central axis is thesame as the rotary axis of the drive shaft 12. The rolling contactsurface of the outer race 10 b is formed in such a manner that diameterof the rolling contact surface of the outer race 10 b on the front sideof the first bearing 10 becomes smaller than that on the rear side ofthe first bearing 10. Each of the rollers 10 c is formed in such amanner that diameter of each of the rollers 10 c on the front side ofthe first bearing 10 becomes smaller than that on the rear side of thefirst bearing 10. That is, each of the rollers 10 c has the shape of acircular truncated cone.

[0021] Referring back to FIG. 1, a lug plate 14 is fixed to the driveshaft 12 in the crank chamber 8 so as to integrally rotate with thedrive shaft 12. A thrust bearing 13 is placed between a front wall ofthe front housing 2 and the lug plate 14 in the crank chamber 8. Thedrive shaft 12 extends though a coned disc spring 20 which is placedbetween the inner race 10 a and the lug plate 14. The coned disc spring20 is served as an urging means. Urging force f0 of the coned discspring 20 is applied to the lug plate 14 rearward.

[0022] Still referring to FIG. 1, a pair of arms 15 protrudes from therear surface of the lug plate 14 rearward, although only one of the arms15 is shown in FIG. 1. A cylindrical guide hole 15 a is formed througheach arm 15. The drive shaft 12 extends through a swash plate 16 where athrough hole 16 a is formed. An inclination angle of the swash plate 16is defined as an angle between a perpendicular plane to the rotary axisof the drive shaft 12 and the swash plate 16. A spring 17 is interposedbetween the swash plate 16 and the lug plate 14 for reducing theinclination angle of the swash plate 16. A return spring 26 isinterposed between the swash plate 16 and a circular clip 25. A bearing27 is placed at the rear end of the drive shaft 12 in the shaft hole 1 bof the cylinder block 1. A support spring 29 is interposed between thebearing 27 and the suction valve plate 3. A regulating member may beused in place of the bearing 27 and the support spring 29.

[0023] A pair of guide pins 16 b protrudes from the front end of theswash plate 16 respectively to the pair of arms 15, although only one ofthe guide pins 16 b is shown in FIG. 1. A spherical guide portion 16 cis formed on the distal end of each guide pin 16 b so as to pivotallyslide along the corresponding guide hole 15 a. The guide holes 15 a ofthe lug plate 15 and the guide portions 16 c of the swash plate 16constitute a hinge mechanism, through which the swash plate 16 isrotated synchronously with the drive shaft 12 and inclines relative tothe drive shaft 12. A plurality of hollow single-head pistons 19 isengaged with the periphery of the swash plate 16. Each piston 19 has apair of shoes 18, which is placed respectively at the front and rearsides of the swash plate 16. Each piston 19 is also accommodated in eachcylinder bore 1 a. A compression chamber 30 is defined on the rear sideof the piston 19 in the corresponding cylinder bore 1 a.

[0024] A pulley 22 is fixed to the front end of the drive shaft 12,which protrudes from the front housing 2 frontward, by a bolt 23. Thepulley 22 is supported by a ball bearing 24 on the front housing 2rotatably. A belt is partially wound around the pulley 22 so as toconnect with an engine EG, which is served as an external drive source.

[0025] In the rear housing 7, a suction chamber 7 a is defined. Thesuction chamber 7 a and the inlet 1 d of the cylinder block 1 arecommunicated via a suction passage, which is not shown in FIG. 1. Thesuction chamber 7 a and the cylinder bores 1 a are communicatedrespectively via suction ports 31, which are formed through the retainerplate 6, the discharge valve plate 5 and the valve hole plate 4. Theinlet 1 d is connected to an evaporator EV of a refrigerant circuit by apiping. The evaporator EV is connected to a condenser CO through anexpansion valve V by a piping. Also, in the rear housing 7, a dischargechamber 7 b is defined around the suction chamber 1 a. The dischargechamber 7 b and the muffler chamber 1 c of the cylinder block 1 arecommunicated via a discharge passage 7 d, which extends through theretainer plate 6, the discharge valve plate 5, the valve hole plate 4and the suction valve plate 3. The muffler chamber 1 c is connected tothe condenser CO of the refrigerant circuit by a piping. The dischargechamber 7 b is connected to the cylinder bores 1 a respectively bydischarge ports 32, which extends through the valve hole plate 4 and thesuction valve plate 3. Further, a control mechanism 34, whichcommunicates with the crank chamber 8, the suction chamber 7 a and thedischarge chamber 7 b so as to control the pressure in the crank chamber8, is accommodated in the rear housing 7. The control mechanism 34 iscapable of adjusting the pressure in the crank chamber 8, for example,by detecting the pressure in the suction chamber 7 a. Thereby, an amountof refrigerant gas discharged from the compression chamber 30 to thedischarge chamber 7 b is varied in accordance with reciprocation of thepiston 19 based on an inclination of the swash plate 16.

[0026] The above structured compressor compresses carbon dioxide filledin the refrigerant circuit. Carbon dioxide is served as a refrigerantgas. Specifically, while the engine EG drives, since the pulley 22 isrotated through the belt, the drive shaft 12 is continuously driven.Thereby, the swash plate 16 is oscillated and the piston 19 isreciprocated in the corresponding cylinder bore 1 a. That is, the piston19 is reciprocated in accordance with the rotation of the swash plate16. Thus, refrigerant gas of the evaporator EV in the refrigerantcircuit is drawn into the suction chamber 7 a through the inlet 1 d andthe refrigerant gas in the suction chamber 7 a is drawn into thecompression chamber 30. After the refrigerant gas in the compressionchamber 30 is compressed therein, the compressed refrigerant gas isdischarged into the discharge chamber 7 b. The refrigerant gas in thedischarge chamber 7 b is discharged into the condenser CO through themuffler chamber 1 c.

[0027] During the compressive process of the compressor, the first andsecond bearings 10 and 11 receive radial force which is applied to thedrive shaft 12 respectively in the front housing 2 and the cylinderblock 1. Also, compressive reaction force of the refrigerant gas istransmitted to the piston 19, the shoes 18, the swash plate 16 and thelug plate 14. Further, in the compressor the crank chamber 8communicates with the shaft hole 1 b of the cylinder block 1 through thesecond bearing 11 and the support spring 29 is interposed between therear end of the drive shaft 12 and the valve mechanism. Therefore, thepressure in the crank chamber 8 is applied to the drive shaft 12 and thelug plate 14. In addition, urging force of the support spring 29 isapplied to the drive shaft 12 and the lug plate 14. Note that the forceapplied to the drive shaft 12 frontward in accordance with the pressurein the crank chamber 8 is f1. Also, note that the urging force of thesupport spring 29 is f2, and that the compressive reaction force is f3.In this case, the urging force f0 of the coned disc spring 20 is set soas to be larger than resultant force of the force f1 which is themaximum value and the urging force f2 of the support spring 29.

[0028] In such a compressor, when a vehicle is stopped and the engine EGis stopped, or when the vehicle is accelerated, or when a vehicle airconditioning system is switched off in a state that the engine EGdrives, the control mechanism 34 raises the pressure in the crankchamber 8. Thereby, the inclination angle of the swash plate 16 becomesminimum. Thus, a volume of the compression chamber 30 becomes minimumand the amount of refrigerant gas discharged from the compressionchamber 30 becomes minimum.

[0029] In the above state of the compressor, the force f1 based on thepressure in the crank chamber 8 becomes the maximum value. The urgingforce f2 is a fixed value. The compressive reaction force f3 is anextremely small value. Meanwhile, when the engine EG and the compressoris started, or when the vehicle is normally run, or when the vehicle airconditioning system is switched on in a state that the engine EG drives,as shown in FIG. 2, the drive shaft 12 is urged frontward by resultantforce of the force f1, the urging force f2 and the extremely smallcompressive reaction force f3. Therefore, the lug plate 14 is also urgedfrontward. In the compressor, however, since the urging force f0 of theconed disc spring 20 is set so as to be larger than resultant force ofthe maximum force f1, which is the maximum value, and the urging forcef2 of the support spring 29, the drive shaft 12 and the lug plate 14 areurged rearward. For this reason, a slight clearance is produced betweenthe lug plate 14, that is, the thrust bearing 13, and the thrust bearing13 does not receive thrust force. Consequently, rolling frictional forceof the thrust bearing 13 is not generated and power loss is reduced.

[0030] In this case, the thrust force which is applied to the coned discspring 20 is received by the first bearing 10 through the inner race 10a. In other words, since the inner race 10 a prevents the coned discspring 20 from sliding over the drive shaft 12, power loss is reduceddue to sliding frictional force. Thus, in this state, only the firstbearing 10 receives thrust force and radial force. Therefore, operationof the compressor is not interrupted. In addition, since the taperedroller bearing is adopted as the first bearing 10, the number of partsis reduced.

[0031] Thus, when the compressor is started in such a manner thatdisplacement of the compressor is minimum, reduction of the power lossaccomplished by the first bearing 10 and the thrust bearing 13 isdescribed as follows. If frictional force generated on the first bearing10 is F1, coefficient of friction of the first bearing 10 is μ1 andthrust force which is applied to the first bearing 10 is N1, F1 givesthe following equation:

F1=μ1×N1

[0032] If the pressure in the crank chamber 8 is P and the diameter ofthe drive shaft 12 is D, the thrust force, which is applied to the firstbearing 10, gives the following equation:

N1=P×π/4×D ²

[0033] Meanwhile, if the rolling diameter of the first bearing 10 is R1,torque T1 which is generated on the first bearing gives the followingequation:

T1=F1×R1

[0034] From the above equations, the torque T1, which is generated onthe first bearing 10, gives the following equation:

T1=μ1×P×π/4×D ² ×R1

[0035] If frictional force generated on the thrust bearing 13 is F2,coefficient of friction of the first bearing 10 is μ2, thrust forcewhich is applied to the first bearing 10 is N2 and the rolling diameterof the second bearing 12 is R2, T2, which is generated on the thrustbearing 13, gives the following equation:

T2=μ2×P×π/4×D ² ×R2

[0036] Thus, gross torque T that are generated on the first bearing 10and the thrust bearing 13 gives the following equation: $\begin{matrix}{T = {{T1} + {T2}}} \\{= {P \times {\pi/4} \times D^{2} \times \left( {{\mu \quad 1 \times {R1}} + {\mu \quad 2 \times {R2}}} \right)}}\end{matrix}$

[0037] In the first embodiment, as described above, when the compressoris started in such a manner that displacement of the compressor isminimum, the torque T2 is not generated on the thrust bearing 13.Therefore, the gross torque T gives the following equation:$\begin{matrix}{T = {T1}} \\{= {{\mu \quad 1 \times P} + {{\pi/4} \times D^{2} \times {R1}}}}\end{matrix}$

[0038] From the above equations, in comparison with a case that torqueis generated on both of the first bearing 10 and the thrust bearing 13,in a case that torque is generated only on the first bearing 10 whoserolling diameter is relatively small, it is found that relatively smalltorque is generated on the drive shaft 12. That is, in the compressor ofthe first embodiment, power loss is reduced. Therefore, when thecompressor is started, load that is applied to the engine EG is reduced.In the compressor especially where carbon dioxide is used as arefrigerant gas in view of environmental problem, the above effect isremarkable.

[0039] On the other hand, in the compressor, if the control mechanism 34lowers the pressure in the crank chamber 8 in a state that the engine EGdrives, the inclination angle of the swash plate 16 becomes maximum.Thus, the volume of the compression chamber 30 becomes maximum and theamount of refrigerant gas discharged from the compression chamber 30becomes maximum.

[0040] In the above state of the compressor, the force f1 becomes aminimum value. The urging force f2 is a fixed value. The compressivereaction force f3 is maximum. Therefore, as shown in FIG. 3, the driveshaft 12 is urged frontward by resultant force of the force f1, theurging force f2 and the maximum compressive reaction force f3.Therefore, the lug plate 14 is also urged frontward. In this case, theurging force f0 of the coned disc spring 20 is defeated because thecompressive reaction force f3 becomes maximum. Thereby, the coned discspring 20 is squeezed between the inner race 10 a of the first bearing10 and the lug plate 14. Thus, the drive shaft 12 and the lug plate 14are urged frontward.

[0041] At this time, while the thrust bearing 13 receives the lug plate14, the urging force f0 of the coned disc spring 20 urges the lug plate14 rearward. Therefore, thrust force which the thrust bearing 13receives is restrained. That is, in the above equation, the torque T2,which is generated on the thrust bearing 13, is reduced. Therefore, inthe compressor of the first embodiment, even in a state that an amountof refrigerant gas discharged from the compressor is relatively large,power loss is reduced. Thereby, while the compressor is driven, loadthat is applied to the engine EG is reduced. Thus, in the compressor ofthe first embodiment, power loss is reduced.

[0042] Further, in the compressor, the coned disc spring 20 is placedwithin a relatively short distance between the inner race 10 a of thefirst bearing 10 and the lug plate 14 and operates the urging force f0therein. Therefore, the length of the drive shaft 12 is shortened.Thereby, a relatively compact compressor is materialized.

[0043] Further, even in a case that an electromagnetic clutch is usedwithout directly placing the pulley 22 around the drive shaft 12 of thecompressor, while the engine EG is connected to the drive shaft 12,similar effects to the above described effects are obtained.

[0044] A variable displacement swash plate type compressor according toa second preferred embodiment of the present invention is also appliedto a vehicle air conditioning system. In the compressor of the secondembodiment, as shown in FIG. 4, a radial bearing 40 and a thrust bearing50 whose rolling diameter is substantially equal to that of the radialbearing 40 are placed in place of the first bearing 10 of the firstembodiment. The rolling diameter of the thrust bearing 50 is smallerthan that of the thrust bearing 13. The radial bearing 40 is placed inthe rear side of the shaft seal device 9. The thrust bearing 50 isplaced in the front side of the coned disc spring 20. In the secondembodiment, identical reference numerals to the first embodiment areapplied to the same or corresponding members in the second embodimentand overlapped description is omitted.

[0045] In the above structured compressor, the thrust bearing 50receives thrust force that is generated on the coned disc spring 20. Theradial bearing 40 receives radial force caused by drive of the driveshaft 12.

[0046] If torque that is generated on the radial bearing 40 is T1 andtorque that is generated on the thrust bearing 50 is T2, as mentionedabove gross torque T gives the following equation: $\begin{matrix}{T = {{T1} + {T2}}} \\{= {P \times {\pi/4} \times D^{2} \times {R1} \times \left( {{\mu \quad 1} + {\mu \quad 2}} \right)}}\end{matrix}$

[0047] where both of rolling diameters of the radial bearing 40 and thethrust bearing 50 are R1.

[0048] Thus, even in the compressor of the second embodiment, grosstorque T is restrained by shortening the rolling diameter of the thrustbearing 50 than that of the thrust bearing 13. Therefore, load that isapplied to the drive shaft 12 is reduced. Thereby, power loss isreduced. Similar effects of the first embodiment are also obtained.

[0049] Therefore, the present examples and embodiments are to beconsidered as illustrative and not restrictive and the invention is notto be limited to the details given herein but may be modified within thescope of the appended claims.

What is claimed is:
 1. A variable displacement swash plate typecompressor used in connection with an external drive source comprising:a housing in which a cylinder bore, a crank chamber, a suction chamberand a discharge chamber are defined; a first bearing accommodated on afront side of the housing, the first bearing receiving radial force andthrust force; a drive shaft supported by the first bearing in thehousing rotatably; a lug plate fixed to the drive shaft in the crankchamber; a swash plate supported by the drive shaft in the crank chamberrotatably; a single-head piston accommodated in the cylinder borereciprocably and connected to the swash plate so as to reciprocate inaccordance with the rotation of the swash plate; a control mechanismcommunicating with the crank chamber, the suction chamber and thedischarge chamber for controlling pressure in the crank chamber; andurging means placed between the first bearing and the lug plate havingurging force for reducing thrust force applied to the first thrustbearing.
 2. The variable displacement swash plate type compressoraccording to claim 1, wherein the drive shaft is urged by a force basedon the pressure in the crank chamber, the urging force being larger thana maximum value of the force based on the pressure in the crank chamber.3. The variable displacement swash plate type compressor according toclaim 1, wherein the first bearing is a tapered roller bearing.
 4. Thevariable displacement swash plate type compressor according to claim 1,wherein the first bearing has a race that is integrally rotated with thedrive shaft, the urging means being a coned disc spring that is placedbetween the race and the lug plate.
 5. The variable displacement swashplate type compressor according to claim 4, wherein the race is an innerrace, the first bearing further having an outer race and a plurality ofrollers, the outer race being press-fitted into the housing, the rollersbeing interposed between the inner race and the outer race.
 6. Thevariable displacement swash plate type compressor according to claim 1,wherein the first bearing has a radial bearing and a second thrustbearing.
 7. The variable displacement swash plate type compressoraccording to claim 6, wherein rolling diameter of the radial bearing isequal to that of the second thrust bearing.
 8. The variable displacementswash plate type compressor according to claim 1, wherein the driveshaft is continuously driven while the external drive source drives. 9.The variable displacement swash plate type compressor according to claim1, wherein the refrigerant gas is carbon dioxide.
 10. A variabledisplacement swash plate type compressor used in connection with anexternal drive source comprising: a housing in which a cylinder bore, acrank chamber, a suction chamber and a discharge chamber are defined,the housing having a front side and a rear side; a first bearingaccommodated on the front side of the housing, the first bearingreceiving radial force and thrust force; a second bearing accommodatedon the rear side of the housing; a drive shaft supported by the firstbearing and the second bearing in the housing rotatably, the drive shafthaving a front end which protrudes from the housing and being driven bythe external drive source; a lug plate fixed to the drive shaft in thecrank chamber so as to integrally rotate with the drive shaft; a firstthrust bearing placed between the front side of the housing and the lugplate in the crank chamber; a swash plate supported by the drive shaftin the crank chamber rotatably; a hinge mechanism interposed between thelug plate and the swash plate, the hinge mechanism through which theswash plate is rotated synchronously with the drive shaft and inclinesrelative to the drive shaft; a single-head piston accommodated in thecylinder bore reciprocably having a rear side, on which a compressionchamber is defined in the cylinder bore, the piston being connected tothe swash plate so as to reciprocate in accordance with the rotation ofthe swash plate; a control mechanism communicating with the crankchamber, the suction chamber and the discharge chamber for controllingpressure in the crank chamber, the control mechanism by which an amountof refrigerant gas discharged from the compression chamber to thedischarge chamber is varied in accordance with the reciprocation of thepiston based on an inclination angle of the swash plate; and urgingmeans placed between the first bearing and the lug plate having urgingforce for reducing thrust force applied to the first thrust bearing. 11.The variable displacement swash plate type compressor according to claim10, wherein the drive shaft is urged from the rear side to the frontside by a force based on the pressure in the crank chamber, the urgingforce being larger than a maximum value of the force based on thepressure in the crank chamber.
 12. The variable displacement swash platetype compressor according to claim 10, wherein the first bearing is atapered roller bearing.
 13. The variable displacement swash plate typecompressor according to claim 10, wherein the first bearing has a racethat is integrally rotated with the drive shaft, the urging means beinga coned disc spring that is placed between the race and the lug plate.14. The variable displacement swash plate type compressor according toclaim 13, wherein the race is an inner race, the first bearing furtherhaving an outer race and a plurality of rollers, the outer race beingpress-fitted into the housing, the rollers being interposed between theinner race and the outer race.
 15. The variable displacement swash platetype compressor according to claim 10, wherein the first bearing has aradial bearing and a second thrust bearing.
 16. The variabledisplacement swash plate type compressor according to claim 15, whereinrolling diameter of the radial bearing is equal to that of the secondthrust bearing.
 17. The variable displacement swash plate typecompressor according to claim 15, wherein rolling diameter of the secondthrust bearing is smaller than that of the first thrust bearing.
 18. Thevariable displacement swash plate type compressor according to claim 1,wherein the drive shaft is continuously driven while the external drivesource drives.
 19. The variable displacement swash plate type compressoraccording to claim 1, wherein the refrigerant gas is carbon dioxide.